mrp: MSRP: bugfix for 4 listener stream case

mrp: MSRP: bugfix for 4 listener stream case

This checkin fixes 2 issues in msrp_emit_listenvectors():
1) when listener streams with incrementing stream ID are registered
the attributes are aggregated, but there was no test for whether the
attribute had already been tx'd, so stream declarations were repeated.
The fix is to mark all attributes for tx before looping through the tx
pack operation and then test the tx flag inside the tx pack loop.
2) incorrect conditional in vect_4pack operation